Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.58   7.501%   $267.226   $267.23   $267.25   $267.20  
  Purchase #2 $12.82   5.856%   $13.5707   $13.57   $13.55   $13.60  
  Purchase #3 $184.64   6.272%   $196.2206   $196.22   $196.20   $196.20  
  Purchase #4 $168.88   13.131%   $191.0556   $191.06   $191.05   $191.10  
  Purchase #5 $18.89   3.402%   $19.5326   $19.53   $19.55   $19.50  
  Purchase #6 $116.44   4.131%   $121.2501   $121.25   $121.25   $121.30  
  Purchase #7 $220.48   9.352%   $241.0993   $241.10   $241.10   $241.10  
  7 purchase totals = $970.73       $1,049.9549   $1,049.96   $1,049.95   $1,050.00